1. Field of the Invention
The present invention relates generally to prism assemblies used in surveying and the like and more specifically to an omni-directional azimuth prism assembly designed to hold a plurality of retro-reflecting prisms distributed symmetrically about the radial wall of a cylinder for reflecting light received from any azimuth direction and over a preselected range of elevation.
2. Prior Art
Retro-reflecting prism assemblies have been used for many years as as adjunct to laser distance measuring instruments in surveying and civil engineering. All such prior art prism assemblies known to the applicant herein, typically provide one or a plurality of prisms all pointed in the same direction for retro-reflection of incident laser light over a limited angle of incidence in azimuth and elevation. Such a substantially uni-directional configuration is perfectly satisfactory for most applications where a measurement of distance between the position of a unitary source of light and the position of the retro-reflector is all that is required. Unfortunately, there occasionally arises the need to provide distance measurement to a fixed retro-reflective position from a variety of light source positions disbursed radially or in azimuth around the location of the retro-reflective prism. For example, one such need arises when the prism assembly is positioned at the center intersection of two or more streets or thoroughfares and it is desired to measure the distance to that center of intersections at displaced points in each of the intersecting streets or thoroughfares. In such applications, it is unlikely that the prism assembly will be properly positioned and directed for all desired positions of the laser light source. As a consequence thereof, each time the measurement is made from a different laser light source location, it is necessary to reorient the direction of the retro-reflective prisms. Thus for example, in a typical case of two streets intersecting at ninety (90) degrees, the prism assembly can be properly positioned only for one of the four possible directions from which the laser light may be emanating. As a result, each time the laser light source is repositioned, it is necessary for personnel to take the time and effort and incur the danger of going to the prism assembly location and reorienting the prism to be directed toward one of the other desired positions of the laser light source.
Typically, there is a sighting target which is associated with the retro-reflective prism assembly in order to reduce the difficulty of pointing the laser light source toward the prism assembly and which, for example, may be as far as a thousand yards from the prism assembly. Like the prism assemblies of the prior art, such sighting targets are also normally designed for unidirectional operation. More specifically, it is typical for such sighting targets to be oriented on the prism assembly in such a way that they face in the same direction as the unidirectional prisms. Accordingly, in applications requiring reorienting the prism assembly such as for the purpose previously described, it would also be necessary to reorient the sighting target to permit sighting of the prism assembly from the laser light source from each of the repositioned locations such as in the intersecting street scenario previously described.
There has therefore been a long felt need for a prism assembly which provides both prisms and sighting target capabilities which permit positioning of a laser light source instrument at any azimuth angle over a 360 degree dispersion relative to the prism assembly for use therewith without requiring reorientation of the prism assembly each time the laser light source is relocated.